The invention relates to intracardiac leads for pacing of the left ventricle. The invention is in the general context of “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 the Council of the European Communities, including implants to continuously monitor heart rhythm and deliver as necessary to the heart electrical stimulation, resynchronization or defibrillation pulses.
Intracardiac “stimulation” leads refers to leads for the delivery of low-energy pulses used for bradycardia or resynchronization therapies. The invention also applies to intracardiac leads for cardioversion/defibrillation intended to deliver a high energy electric shock to the heart to try to terminate a tachyarrhythmia. “Stimulation lead (or electrode)” or “stimulation/defibrillation lead” may refer to any kind of lead used for these or other similar purposes.
For stimulation of the right ventricle, the implantation of an endocardial lead through the right peripheral venous network is sufficient. However, to stimulate the left ventricle, the situation is more complex. The most commonly adopted solution is to introduce a lead, not into the cavity to stimulate, but in the coronary network, the lead being provided with an electrode applied against the wall facing the epicardium and oriented in direction of the left ventricle. These leads stimulate the heart muscle via one or more point electrodes, the position of which is a function of the predefined trajectory of the cannulated vein. A lead of this type is for example the Situs LV model marketed by Sorin CRM (Clamart, France) and described in EP 0993840 A1 (ELA Medical). The introduction of such a lead is made via the coronary sinus, because of its opening in the right atrium. The lead is then pushed and oriented along the network of coronary veins to the selected site. Once the target vein is reached, the surgeon looks for a satisfying stimulation site, and with a good electrical contact of the stimulation electrode against the tissue of the epicardium. This contact is maintained despite various variations or stresses over time. This implantation technique is not always feasible, especially when the shape of the coronary sinus is too rough, or in case of thrombosis. Indeed, the precise positioning of the electrode(s) to stimulate the left ventricle through the myocardial wall is a critical parameter, and it is not always possible to reach effective stimulation sites.
Another more difficult and much more invasive technique involves an implantation of epicardial electrodes on the outer wall of the myocardium, in one or more suitable sites facing the cavity of the left ventricle. A variant of this technique, described in EP 2308550 A1 (Sorin CRM), involves the implantation of the electrode, formed by the conductive helical screw of a screw lead, via a bent catheter inserted into the pericardial sac. However, these techniques are relatively invasive and also generally irreversible, since it is very difficult to change the implantation site initially chosen, and to explant, if necessary, the lead at a later stage.
Another approach, to which the invention pertains, is to stimulate the left ventricle by applying pacing pulses to the wall of the interventricular septum (the wall separating the left ventricle and the right ventricle) by means of a lead inserted into the right ventricle using a traditional approach. This technique involves the drilling of the atrial or ventricular septum, then the introduction of a lead through this septum until it comes into contact with a point on the wall of the left ventricle. The stimulation pulses are then applied directly to the left endocardial site thus selected. For an example of a controlled transeptal puncture technique, one may refer to EP 1516644 A1 (ELA Medical), which describes a guiding accessory having one end closed by an anchoring screw to the right wall of the septum, and in which a piercing stylet is inserted for initiating a puncture of the septum. After withdrawal of the piercing stylet, a guiding stylet is inserted in the accessory, to form an axial guide in which the pacing lead, provided with its electrodes, is then introduced in the left cavity after removal of the accessory.
Another technique for making a transeptal puncture, described by EP 2327366 A1 (Sorin CRM) is to anchor a screw to the septum wall, and then to apply to this screw radiofrequency energy to progressively sink into the septum wall until it passes through the latter. The puncture can also be performed by a guide-wire supplied with the RF energy, which is pushed to cross from one side to the other the septum.
These techniques have several drawbacks, mainly due to the fact that they require making a puncture in the septal wall of a diameter sufficient to insert a guide-catheter for establishing a communication between the right and left cavities through the wall, to then insert the left endocardial stimulation lead. Because the element opening into the left ventricle element is a hollow catheter, this results in significant risk of air embolism. To avoid this risk, it is imperative to take many precautions when handling haemostatic valves, meeting purge equipment procedures, etc. However, given the highly invasive nature of the procedure, uncertainties remain about the behavior in the long-term blood circulation, which involves anticoagulation to prevent thromboembolism postoperatively. Finally, subsequent extraction of the lead is practically impossible, because of the excessive risks that would be incurred at the crossing of the septum.
In any case, these techniques are very difficult to implement and require great skill of the practitioner, who, before crossing the septum, must always ensure perfect positioning of the piercing needle on the wall, crossing the septum having to be undertaken only if there is not any doubt left about the position of the needle, to avoid accidental dissection of the walls by a sudden movement of the needle piercing the septum—hence the development of specific drilling kits, such as those described in EP 1516644 A1 and EP 2327366 A1 above.
Yet another technique designed to reduce these risks is described by EP 2457612 A1 and EP 2384784 (Sorin CRM). The basic idea is to remove the guide catheter associated to a lead crossing the septum, and replace this set by a conventional lead screwed onto the wall of the right ventricle at the septum, extending the lead by a transeptal microcable, partially isolated and pushed into the left ventricle to come into contact against a target located in this ventricle, for example against the free wall of the latter (that is to say the wall located opposite to the septal wall).
Due to the extreme thinness of the puncture (the size of which being that of the microcable diameter), this technique greatly reduces the risks associated with previous techniques. However, insofar as the microcable is freely deployed in the left ventricle, it is difficult to control the delivery of pacing pulses at specific sites, and to ensure adequate and continuous contact between the electrodes of this free part and the wall of the left ventricle because of the physical instability of the microcable on the free wall resulting from the very high flexibility of the microcable. In addition, the transmission of the puncture push via the microcable can be difficult: indeed, the need for mechanical endurance requires great flexibility for the microcable, flexibility that is not compatible with the necessary requirement of “pushability” (ability to transmit axial pushing forces applied from the proximal end) during the puncture step.